The test CD will get you in the general area of where the resonance is.

http://www.linearteam.dk/

Download the WinISD pro program and install it. It has sine wave output capability. you just drag a mouse on a graph and a tone is produced. You can pipe this tone into a amplifier from your computer and determine the port frequency.
Even ifyou make ports like recommended itmay not be right. You have to test.

Your ports are way too small, enlarging them is good because the large woofer needs a large port to prevent Power Compression.